1. Field of the Invention
The present invention relates to a cord and, more particularly, to a cord suitably used as a vehicle tire reinforcing material.
2. Description of the Prior Art
A typical conventional tire cord for reinforcing a rubber tire is known, as shown in FIG. 1. In the tire cord, nine peripheral wires .delta..sub.1 surround three core wires .delta..sub.0. Wires .delta..sub.1 and .delta..sub.0 are twisted together in one direction to obtain a stranded cord. Wires .delta..sub.1 and .delta..sub.0 have the same diameter. As is apparent from FIG. 1, wires .delta..sub.0 are in tight contact with each other, and at the same time wires .delta..sub.1 are in tight contact with each other.
A tire cord embedded in a rubber tire is subjected to repeated bending with compression and tension during rotation of the tire. In the conventional cord described above, displacements of the peripheral wires differ from each other due to changes in compression and tensile stresses, and the adjacent peripheral wires are undesirably brought into contact to cause fretting wear, thereby increasing fatigue of the wires. Since the peripheral wires are in contact with each other, they cannot apply a large tightening force to the core wires. For this reason, the core wires are deviated from the initial positions, and ends of the core wires may stick out from the tire cord to cause a decisive defect in the tire.
In the conventional tire cord described above, since the peripheral wires are in tight contact with each other, rubber cannot sufficiently reach inside the cord due to poor rubber filling. Thus, if the tire is under bad conditions, e.g., if a rubber layer of the tire is damaged, moisture permeates into the cord through the damaged portion of the tire. As a result, the cord rusts, adhesion between the cord and the rubber layer is degraded, and a separation phenomenon occurs.